The manufacture of valves for internal combustion engines has had to keep pace with the drastic changes in auto engines. For example, with the introduction of low lead gasoline and the use of high compression engines, valves previously acceptable were no longer suitable. It was required to drastically modify valve manufacturing procedures to provide acceptable valves having improved wear properties while workable within the small tolerances allowed in combustion chambers. Various valve coatings have been used such as nickel, chrome, nitride and other known coating materials. A problem encountered in these processes is to obtain a thick enough coating to minimize corrosion and yet function within tolerances required in these advanced engines. Uniformity of coating and a smooth valve coating surface are properties that enhance the adaptability of these valves. The requirements of today's engines has caused increased problems for everyone involved in engine manufacture. The increase in running temperatures, lightweight blocks and heads and no-lead fuels have placed a high demand on manufacturers to develop superior designs and materials to operate under tougher conditions and more economically than they did in the past. In addition to these demands, when it comes time to rebuild the engine, it is necessary to stick to the proper specifications and proper material for each application of the engine.
The area of concern that is becoming a big issue is proper valve life. Valve open and close 25 times a second when the engine is operating at 3,000 RPM. That is a tremendous amount of movement when you consider the valve receives the least amount of lubrication of all the other internal moving parts of the engine. This means that the valve, seat, guide and geometry must all be correct and working properly for the valve to survive. The four main causes of premature valve failure are geometry, clearance, material and heat. The geometry of the valve and rocker is a difficult measurement to calculate, however, it is important. When the geometry is incorrect, it causes uneven wear of the valve stem and guide which results in engine failure. As the guide wears, the clearances increase which will cause excess oil consumption. More serious and costly damage is caused when improper geometry causes the valve to close off center of the seat resulting in valve stem fatigue at the head and keeper groove areas of the valve. This leads to the valve breaking.
Various suggestions have been made to provide adequate valves for today's engine use. In U.S. Pat. No. 5,190,002 (Wietig) a valve having cross-hatching was disclosed, said cross-hatching having a depth sufficient to maintain lubrication while at the same time smooth enough to provide minimal wear on contacting parts. In U.S. Pat. No. 4,811,701 (Buhl) coated valves are disclosed using cerium oxide coatings ad a process for effectuating this coating is given. In U.S. Pat. No. 2,664,873 (Graham) a coated valve is disclose having coatings in the thickness range of between 0.001 to 0.015 inch. Graham suggests that alloys containing aluminum and nickel either alone or together with other constituents be used. The use of these metals as coatings within 0.001 to 0.015 inch, Graham suggests, would provide valve bondings to the base metal. A method for coating the valve is disclosed by Graham to include etching the valve with sulfuric acid and depositing the nickel electrolytically. While Graham's 1954 coated valves were adequate for resisting corrosion and proper engine clearances, these valves would not function in today's advanced engines. The engine requirements in 1954 were far less demanding tan are the requirements of today's high compression engines. Also, electrolytic nickel coating of valves would not be acceptable today primarily because of the non-uniformity of the valve coatings.
A coated valve is required that gives a proper balance between a thickness as that will prevent corrosion and wear and yet will not interfere with valve stem to guide clearance.
Electroless Nickel can protect the base valve from serious corrosive attack. The 1990 Clean Air Act requires the automotive industry to reduce emissions and one possibility can be to utilize methanol fuel blends. However, a major drawback is the extreme corrosive nature these fuels have on currently designed vehicles. Electroless Nickel on steel demonstrated the best corrosion performance under controlled test conditions of CM85A and CM85AP fuels better than stainless steel 304 because it is a barrier coating and can be applied to the entire valve without disturbing its tolerance.